Including a value once in a summed SSRS group - reporting-services

Question

I have a data source which is pulling in event attendance information which looks like the following table.
Note that one booking can contain multiple attendees, causing duplication in the Amount column.
+------------+-----------+---------------+----------+
| Date | Booking | Booking Price | Attendee |
+------------+-----------+---------------+----------+
| 01/01/2011 | Booking 1 | £300.00 | Alice |
| 01/01/2011 | Booking 1 | £300.00 | Bob |
| 01/01/2011 | Booking 1 | £300.00 | Dave |
| 01/01/2011 | Booking 2 | £200.00 | Frank |
| 01/01/2011 | Booking 2 | £200.00 | Julie |
| 02/01/2011 | Booking 3 | £100.00 | Anne |
+------------+-----------+---------------+----------+
The Report should end up a bit like this:
+------------+-----------+---------+
| Date | Booking | Amount |
+------------+-----------+---------+
| 01/01/2011 | Booking 1 | £300 |
| | Alice | |
| | Bob | |
| | Dave | |
+------------+-----------+---------+
| | Booking 2 | £200 |
| | Frank | |
| | Julie | |
+============+===========+=========+
| TOTAL FOR 01/01/2011 | £500 |
| |
| |
+============+===========+=========+
| 02/01/2011 | Booking 3 | £100 |
| | Anne | |
+============+===========+=========+
| TOTAL FOR 02/01/2011 | £100 |
| |
| |
+============+===========+=========+
(That pretty much exhausts my ascii-art table skills!)
The problem I have is that because the amount is showing for each delegate, the aggregate functions count them all, so date for 01/01/2011 shows as £1300, instead of £500
I don't need any values next to the attendees, so I could pull it in a separate data set, but I can't seem to add a table into a tablix cell, so don't know how that would work.

Answer 1

The version of SSRS is key here. In SSRS 2008R2, you can now nest aggregate functions:
So this would now be a valid expression:
=SUM(FIRST(Fields!BookingPrice.Value , "BookingGroupName") , "DateGroupName")
If you aren't yet on 2008R2 then you can do some tricks with embedded code to keep a running total: http://beyondrelational.com/blogs/jason/archive/2010/07/03/aggregate-of-an-aggregate-function-in-ssrs.aspx
The key here is that you add to the total in the embedded code once per group. Then retrieve the total and clear it out at the end of the group.